Maintaining an optimal climate in museum collections can be extremely tricky. Everything from the general climate of the region to types of items in the collection to the comfort of museum visitors and employees must be taken into account. Relative humidity is one key consideration.
According to an article by the Northern States Conservation Center that addresses temperature and relative humidity levels for museum objects, “there is no single relative humidity range that is ideal for all museum objects.” However, NSCC does recommend maintaining a non-fluctuating relative humidity (RH) above 25% and below 65% for mixed collections — noting that many museums maintain an RH of 45%.
Keeping a consistent relative humidity is crucial, as an RH below 25% “can cause embrittlement of hygroscopic materials such as leather and paper,” and an RH above 25% can lead to mold growth and metal corrosion.